1. Field of the Invention
This invention relates to electrowinning and electrorefining processes which employ alternating cathode and anode plates positioned in an electrolytic solution, and specifically relates to integrally formed frames for retaining a cathode plate therein.
2. Description of Related Art
Many mining and metallurgical operations employ electrolytic processes to recover or refine metals, such as cobalt or zinc. The primary electrolytic processes that are used in such operations are electrowinning, electrorefining or a combination of those two. In electrowinning, metals are typically recovered from an electrolyte solution containing such metals using an insoluble anode and a cathode having a starter sheet made of the same metal as that being recovered, or another suitable material. In electrorefining, purified metal is transferred from the anode, which is made at least in part from the metal, through the electrolyte to the cathode. In both electrowinning and electrorefining, the recoverable or refinable metal is plated or otherwise adhered to the cathode starter sheet. In some operations, a combination of electrowinning and electrorefining processes may be employed to recover metals. For example, a target metal may be transferred from a soluble anode positioned in tank to the surrounding electrolyte, which is then piped from the tank into an isolated cathode starter sheet to facilitate electrowinning of the metal from the electrolyte solution.
In any of the processes previously described, vertically-oriented anode plates and cathode plates are typically arranged side-by-side in alternating arrangement within a tank sized to receive the anode and cathode plates. The anode, and particularly the cathode plate, may be positioned within a frame to maintain it in vertical orientation and in proper proximity to the next adjacent anode or cathode. Depending on the processes being carried out and the metal being recovered or refined, the anode, cathode or both, may be covered with a permeable media which allows metal ions to pass through the media into the electrolyte, but which does not allow impurities or other material to pass through to the electrolyte. The tank holds the electrolyte solution in which the anode and cathode plates are positioned. A certain level of electrolyte may typically be maintained in the tank to facilitate the recovery or refining of metals.
After sufficient time has passed for the recovery or refining of metal on the cathode plate, the cathode frame and plate are removed from the tank so that the metal deposits from the cathode starter sheet, or plate, can be recovered. The cathode plate must be removed from the surrounding frame to access the deposited metals, but the build-up of metal on the initial starter sheet often makes it difficult to remove the cathode plate from the cathode frame. Hence, it is quite common for the technicians to pound, hammer or beat on the cathode frame in an effort to separate or dislodge the cathode plate from the frame.
Early cathode frame designs were conventionally manufactured from wood or relatively durable plastic material and the frames comprised edge sticks or strips which were positioned along each of the three submerged sides of the cathode plate. Examples of such cathode frames are disclosed in, for example, U.S. Pat. No. 4,282,082 to Cook, et al.; U.S. Pat. No. 4,288,312 to Johnson, et al.; U.S. Pat. No. 4,776,928 to Perlich; U.S. Pat. No. 5,314,600 to Webb, et al. and U.S. Pat. No. 5,690,798 to Alexander, et al. However, the deposition of metal on the starter sheet made removal of the cathode plate from the frame very difficult.
In more recent years, the conventional edging strips used to mask the edges of the cathode plate have been configured to join or abut each other to enclose the peripheral edge of that portion of the cathode plate which is submerged. The intersecting or abutting edges of adjacent edge strips have typically been sealingly joined, such as with adhesives, to secure the edge strips together and to prevent electrolyte from seeping between abutting edges. Such construction has been considered to be more efficient and economical in terms of manufacture and maintenance of the cathode frame. However, it has also been recognized that the adhesive or other bonding method used to join the abutting edge strips eventually dissolves or degrades over time, thereby allowing electrolyte to seep between the edge strips and the integrity of the frame as a whole is compromised. U.S. Pat. No. 5,690,798 proposes a solution to the problem by providing corner protectors which are structured to receive the ends of edge strips which form the sides and bottom of the frame. The ends of the edge strips are inserted into the corner protectors and are adhesively joined together. The corner protector is described as providing a friction fit with the edge strips to, presumably, prevent electrolyte from seeping between the corner protector and the edge strip.
As previously noted, when the cathode frame and plate are removed from the tank for recovering the deposited metal, the deposition of the metal makes removal of the cathode plate from the frame very difficult, and it is common to have to resort to extreme measures to remove the plate from the frame. Most commonly, the top outer corners or sides of the frame are hammered repeatedly until the plate gives way from the frame. However, the extreme measures of hammering or pounding on the frame frequently cause the frame to break or crack, typically at the point of joinder of the separate side and/or corner elements where the adhesive has degraded. Additionally, wooden frames are unable to withstand the extreme abuses employed to remove the plate from the frame and are equally weakened by the acidic environment of the electrolyte. The development of unitarily formed frames has enabled a marked improvement in maintaining the integrity of cathode frames; however, damage still occurs when the frames are hammered as described.
Thus, it would be advantageous in the art to provide a cathode frame which is especially designed and structured to withstand the normal abuses to which cathode frames are subjected, thereby increasing the useful life of the cathode frame, and to structure a cathode frame which will withstand the harsh environment of the electrolytic process.